Patients at United Nations mental institutions in Kosovo have been raped and physically attacked under the eyes of UN staff, held in "filthy and degrading" conditions, and threatened with punishment if they report the abuses, according to a damning investigation published in New York yesterday.

In one case, a woman patient was raped after UN employees locked her in a room with a male patient because they wanted to "calm her down", while employees who observed another rape in a hallway said they did not intervene because the victim "must have asked for it", according to the independent campaigning group Mental Disability Rights International (MDRI), which produced the report.

"This is a pervasive pattern of serious abuses. The rule of law simply does not apply within these psychiatric facilities," Dr Eric Rosenthal, MDRI's founder, said yesterday. "We found extreme, inhuman and degrading treatment, arbitrary detention and the physical and sexual assault of women, and we received a blanket denial from the authorities."

Dr Robert Okin, chief psychiatrist at San Francisco's biggest hospital and one of the report's authors, said the UN had "disregarded its own standards for the protection and treatment of the mentally disabled and turned a blind eye to the evidence" at Kosovo's two mental institutions - the Shtime home, which houses 285 patients 19 miles south of Pristina, and the Pristina elderly home - and the Pristina University hospital.

In the course of the two-year study, investigators at Shtime reported finding patients sleeping on concrete floors amid piles of human excrement, or in soiled sheets, and spending their days in apathy, sometimes without clothing, and often with nothing to do. They were given out-of-date psychotropic drugs with no monitoring by experts, because there is no psychiatrist on staff.

In further reports of sexual assault, male patients were allowed to roam the women's wards at night making what one Red Cross worker called "voluntary or involuntary girlfriends".

Kosovo's director of psychiatric institutions told MDRI he did not have the money available to fit a secure door to protect the women's wards, even though funds were available for refurbishment elsewhere in the facility, the group said.

An official at the United Nations Mission in Kosovo (Unmik), which holds overarching responsibility for the government of the former Yugoslav province, admitted the report was "not generally inaccurate".

The campaigners condemned the UN for continuing to fund refurbishment of the institutions instead of integrating the patients into community care programmes, but the official said money was not available for such initiatives. In addition, the patients were mostly ethnic Serbs, while the surrounding community was mostly ethnic Albanian, and the patients might be "abused or killed" if released.

"This is not in any way to excuse the bad circumstances in the institutions, but it's not like New York or California." But the official agreed that many ethnic Albanian staff had "not been trained and probably [were] not very sympathetic" to the patients.

Another UN official said the organisation intended to "explore and examine" individual allegations, but money might prevent it. "The question is, do we have the resources that are sufficient to follow the recommendations in the report?" the official said.

Later, in a statement, Unmik said: "We are in the process of developing special programmes to alert nurses and staff to the issue," adding that "children have been removed from the institution at Shtime and are no longer vulnerable". But "to build up a structure and mechanisms to deal with this phenomenon at the local level... takes time".

Dr Rosenthal said that patients had been warned by staff to keep quiet. "If you say anything bad about the staff, God will kill you," a nurse was reported as telling a patient in front of an MDRI investigator at Pristina University hospital.

Two former patients there, along with a physician working for another organisation, were also threatened by a staff member to prevent them revealing that the staff member had had sexual relationships with the two patients, the report said.

Furthermore, "when women have been diagnosed as mentally ill, they are no longer credible as witnesses to the abuse", said Laura Prescott, one of the report's authors and president of Sister Witness International, a US organisation founded by formerly institutionalised women.

Dr Okin said UN bureaucracy prevented the organisation from hiring a foreign psychiatrist. There were no psychiatrists at Shtime because "the UN is strangled by its own version of a civil service bureaucracy: its pay classification system is such that it won't allow itself to pay for a psychiatrist", he said.

The report, funded by the Open Society Institute with money from financier George Soros, was endorsed by the most respected human rights organisation in the US yesterday. Kenneth Roth, executive director of Human Rights Watch, called it "profoundly important... the horrors it describes are undeniable".